[PATCH 09/14] iomap: Change iomap_write_begin calling convention

Matthew Wilcox (Oracle)
2020-10-14T09:30:44Z

Pass (up to) the remaining length of the extent to iomap_write_begin()
and have it return the number of bytes that will fit in the page.
That lets us copy more bytes per call to iomap_write_begin() if the page
cache has already allocated a THP (and will in future allow us to pass
a hint to the page cache that it should try to allocate a larger page
if there are none in the cache).

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
fs/iomap/buffered-io.c | 61 +++++++++++++++++++++++-------------------
1 file changed, 33 insertions(+), 28 deletions(-)

diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 4ef02afaedc5..397795db3ce5 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -616,14 +616,14 @@ iomap_read_page_sync(loff_t block_start, struct page *page, unsigned poff,
return submit_bio_wait(&bio);
}

-static int
-__iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
- struct page *page, struct iomap *srcmap)
+static ssize_t __iomap_write_begin(struct inode *inode, loff_t pos,
+ size_t len, int flags, struct page *page, struct iomap *srcmap)
{
loff_t block_size = i_blocksize(inode);
loff_t block_start = pos & ~(block_size - 1);
loff_t block_end = (pos + len + block_size - 1) & ~(block_size - 1);
- unsigned from = offset_in_page(pos), to = from + len;
+ size_t from = offset_in_thp(page, pos);
+ size_t to = from + len;
size_t poff, plen;

if (PageUptodate(page))
@@ -658,12 +658,13 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
return 0;
}

-static int
-iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
- struct page **pagep, struct iomap *iomap, struct iomap *srcmap)
+static ssize_t iomap_write_begin(struct inode *inode, loff_t pos, loff_t len,
+ unsigned flags, struct page **pagep, struct iomap *iomap,
+ struct iomap *srcmap)
{
const struct iomap_page_ops *page_ops = iomap->page_ops;
struct page *page;
+ size_t offset;
int status = 0;

BUG_ON(pos + len > iomap->offset + iomap->length);
@@ -674,6 +675,8 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
return -EINTR;

if (page_ops && page_ops->page_prepare) {
+ if (len > UINT_MAX)
+ len = UINT_MAX;
status = page_ops->page_prepare(inode, pos, len, iomap);
if (status)
return status;
@@ -685,6 +688,10 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
status = -ENOMEM;
goto out_no_page;
}
+ page = thp_head(page);
+ offset = offset_in_thp(page, pos);
+ if (len > thp_size(page) - offset)
+ len = thp_size(page) - offset;

if (srcmap->type == IOMAP_INLINE)
iomap_read_inline_data(inode, page, srcmap);
@@ -694,11 +701,11 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
status = __iomap_write_begin(inode, pos, len, flags, page,
srcmap);

- if (unlikely(status))
+ if (status < 0)
goto out_unlock;

*pagep = page;
- return 0;
+ return len;

out_unlock:
unlock_page(page);
@@ -854,8 +861,10 @@ iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,

status = iomap_write_begin(inode, pos, bytes, 0, &page, iomap,
srcmap);
- if (unlikely(status))
+ if (status < 0)
break;
+ /* We may be partway through a THP */
+ offset = offset_in_thp(page, pos);

if (mapping_writably_mapped(inode->i_mapping))
flush_dcache_page(page);
@@ -915,7 +924,6 @@ static loff_t
iomap_unshare_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
struct iomap *iomap, struct iomap *srcmap)
{
- long status = 0;
loff_t written = 0;

/* don't bother with blocks that are not shared to start with */
@@ -926,25 +934,24 @@ iomap_unshare_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
return length;

do {
- unsigned long offset = offset_in_page(pos);
- unsigned long bytes = min_t(loff_t, PAGE_SIZE - offset, length);
struct page *page;
+ ssize_t bytes;

- status = iomap_write_begin(inode, pos, bytes,
+ bytes = iomap_write_begin(inode, pos, length,
IOMAP_WRITE_F_UNSHARE, &page, iomap, srcmap);
- if (unlikely(status))
- return status;
+ if (bytes < 0)
+ return bytes;

- status = iomap_write_end(inode, pos, bytes, bytes, page, iomap,
+ bytes = iomap_write_end(inode, pos, bytes, bytes, page, iomap,
srcmap);
- if (WARN_ON_ONCE(status == 0))
+ if (WARN_ON_ONCE(bytes == 0))
return -EIO;

cond_resched();

- pos += status;
- written += status;
- length -= status;
+ pos += bytes;
+ written += bytes;
+ length -= bytes;

balance_dirty_pages_ratelimited(inode->i_mapping);
} while (length);
@@ -975,15 +982,13 @@ static s64 iomap_zero(struct inode *inode, loff_t pos, u64 length,
struct iomap *iomap, struct iomap *srcmap)
{
struct page *page;
- int status;
- unsigned offset = offset_in_page(pos);
- unsigned bytes = min_t(u64, PAGE_SIZE - offset, length);
+ ssize_t bytes;

- status = iomap_write_begin(inode, pos, bytes, 0, &page, iomap, srcmap);
- if (status)
- return status;
+ bytes = iomap_write_begin(inode, pos, length, 0, &page, iomap, srcmap);
+ if (bytes < 0)
+ return bytes;

- zero_user(page, offset, bytes);
+ zero_user(page, offset_in_thp(page, pos), bytes);
mark_page_accessed(page);

return iomap_write_end(inode, pos, bytes, bytes, page, iomap, srcmap);
--
2.28.0